The present invention relates to a manufacturing method of a transition critical refrigerating cycle device having a supercritical pressure on a high-pressure side.
In recent years, considering from a global environment problem, a refrigerating cycle device has been developed in which, for example, carbon dioxide (CO2) is used as a refrigerant (see, e.g., Japanese Patent Application Laid-Open No. 2005-188924). In a case where carbon dioxide is used as the refrigerant, a transition critical cycle is achieved in which a refrigerating cycle on a high-pressure side is supercritical. Therefore, in a device in which a cooling function of en evaporator is used for a purpose of refrigerating, freezing or cooling, the refrigerant needs to be more efficiently cooled with a gas cooler to release more heat.
On the other hand, since such a refrigerating cycle on the high-pressure side has a remarkably high pressure, a second-stage compressor is usually used as a compressor constituting the cycle. Furthermore, to improve a compression efficiency of high-stage compression means of this compressor, in this type of device, a sub-cooler is used which cools the refrigerant before the refrigerant is discharged from low-stage compression means and sucked into the high-stage compression means.
This sub-cooler is usually integrated with the gas cooler to constitute one heat exchanger. In this case, the heat exchanger is constituted of a plurality of refrigerant pipes and a fin for heat exchange through which these pipes pass. End portions of the refrigerant pipes are connected to one another via bend pipes (this bend pipe is integrated with the refrigerant pipe, i.e., the refrigerant pipe is sometimes constituted by bending the pipe) to thereby constitute a meandering refrigerant passage. Moreover, a part of the refrigerant pipes are used in the sub-cooler, and the remaining refrigerant pipes are used in the gas cooler.
On the other hand, the gas cooler and the sub-cooler need to cool the refrigerant as much as possible as described above. Therefore, it is preferable to enlarge the heat exchanger. However, since there is a restriction on a space for an actual device, the number of the refrigerant pipes is limited. Therefore, it is necessary to appropriately set a ratio between the number of the refrigerant pipes for the gas cooler and the number of the refrigerant pipes for the sub-cooler in one heat exchanger. That is, when the gas cooler uses a large number of refrigerant pipes, a cooling capability of the refrigerant of the sub-cooler falls short. Conversely, when the gas cooler uses a small number of refrigerant pipes, less heat is radiated from the refrigerant of the gas cooler, and cooling cannot sufficiently be performed.